1. Field of the Invention
2. Related Art
As shown in FIG. 5, generally, in a structure of an armature 50 of a small brush DC motor of a 4-6 (4-magnetic-polexe2x80x946-salient-pole) structure, for wiring of coils 53 wound around six radially projecting salient poles 52 of an armature core 51 and six risers 55 electrically conducting as terminals of six commutators 54, a circuit is previously formed with a substrate or electrode print pattern 57 (hatched portion in the figure) formed as a thick film on one side of a ring varistor 56, the windings of the coils 53 wound around the six salient poles 52 are connected to the six risers 55 extended from the corresponding six commutators 54, and the electrode print pattern 57 of the ring varistor 56 are joined to the faces of the risers 55 by soldering 58, forming the armature 50.
The electrode print pattern 57 illustrated in FIG. 5 is a circuit pattern conducting so that a pair of two long and short risers formed interposing the rotation center of the armature therebetween becomes the same potential; three circuit patterns for the three pairs of risers are formed in the same shape and electrically independent of each other.
That is, the circuit pattern for electrically connecting a pair of risers, for example, extends from one long riser round the outside of a short riser in another pair adjacent to the pair through the lower side of a long riser in still another pair adjacent the pair to the associated short riser. The three circuit print patterns 57 are formed on one side of the ring varistor 56 and a pair of long and short risers is connected by soldering 58 for each print pattern 57. Further, the three circuit patterns are placed so as to separately contain three electrodes disposed in the ring varistor 56 and are electrically connected.
The above-described wiring structure uses the circuit formed in the ring varistor 56 as a part of a current diverting circuit of the coil 53 by the commutator 54.
However, to flatten and miniaturize a motor, it is difficult to place the electrode print pattern 57 in the ring varistor 56 and the ring varistor 56 is specifically designed and manufactured; it is unavoidable that the product becomes expensive.
Further, if the electrode print pattern 57 placed in the ring varistor 56 becomes small, it easily comes in contact with another pattern and positioning accuracy with the risers 55 becomes strict; it is feared that an electric short circuit may be produced when coil terminals are connected or soldered.
It is therefore an object of the invention to apply a normal ring varistor provided with three electrodes used with a general armature of a 2-3 (2-magnetic-polexe2x80x943-salient-pole) structure having three electrode parts in an armature in a 4-6 structure. It is accomplished by a coil winding method around salient poles that a normal 3-electrode varistor provides an overvoltage suppression effect equal to that of a varistor specifically designed for an armature of a 4-6 structure.
It is more particularly to solder three of six risers directly to three electrodes of a varistor together with coil winding terminals and solder only coil winding terminals to the remaining three risers each between the electrodes of the varistor for forming an armature, in short, route a coil winding around salient poles in a manner of drawing with a single stroke of a brush containing connection to the risers.
According to an aspect of the present invention, there is provided a small motor comprising:
an armature having six salient poles radially and a coil wound around the salient poles;
six risers connected to said coil;
commutators being joined to said risers in a one-to-one correspondence;
a ring varistor being connected to said riser for suppressing overvoltage;
a brush coming in sliding contact with said commutator for supplying a current; and
a permanent magnet having four magnetic poles, placed facing the salient poles,
wherein said coil includes one wire wound continuously around the six salient poles and the six risers from a winding start terminal to a winding end terminal and said ring varistor is provided with three electrode parts to which alternate three of said six risers are connected.
As described above, according to the small motor according to the invention, a general ring varistor used with an armature of a 2-3 (2-magnetic-polexe2x80x943-salient-pole) structure can be applied to a device for extinguishing spark arcs for suppressing overvoltage of an armature of a 4-6 (4-magnetic-polexe2x80x946-salient-pole) structure without special working and moreover a special wiring pattern is not used, thus part-to-part accuracy is not required and the structure and parts management can be simplified sufficiently.
Because of coil winding according to a pattern drawn with a single stroke of a brush, automation is facilitated and productivity can be improved. Further, the varistor can be miniaturized, so that the armature itself can be well fitted to miniaturization.